1. Field of the Invention
This invention relates to polymeric compositions for lining pipe.
2. Description of the Prior Art
Pipe has been used in transporting water and other liquids for many centuries. Pipe is also used in the water transport of sewage, coal, ores and the like. The replacement of buried pipe used for such purposes is difficult, especially where there are existing networks of pipe, wiring and buildings and other structures which must not be disturbed. More recently it has been proposed to in situ line pipe now in service to avoid the problems associated with removal of damaged underground piping. Methods and apparatus for lining horizontal sections of sewer pipe are known, for example from U.S. Pat. No. 4,985,196, and the prior art referred to therein which is incorporated herein by reference. Unfortunately, the compositions for and methods of relining the pipe leaves much to be desired. Among other things, it is desirable to provide shorter installation times, lower temperature and lower installation pressures on the liner and better fit of the liner. Linings based on epoxy compositions typically require a 24 hour cure period prior to resuming use of the sewer pipe. Liners based on polyethylene compositions require higher temperature and pressures to obtain a reasonable installation. Failure to tightly fit the liner to the wall of the pipe allows for continued infiltrating of soil water and other runoff fluids into the pipe and eventually into the sewage treatment plant. A fully fitted liner avoids the extra load placed on sewage treatment plant by rain and the like.
Polyvinyl chloride (PVC) pipe currently being used as a pipe liner for sewer rehabilitation is in the form of a rigid thermoplastic PVC which has a flexural modulus of greater than 300,000 psi and a glass transition temperature of 70.degree. C. and higher. A particular problem associated with the PVC pipe liners of the prior art occurs upon following the formation of the pipe liner by conventional extrusion processes and winding the pipe liner while still pliable onto rolls for storage. Upon cooling, the PVC becomes extremely stiff and cannot effectively be removed from the storage means or roll even at ambient temperatures of 70.degree. or greater. It therefore becomes necessary that the rolled pipe liner in its stored condition must be heated at a temperature of approximately 300.degree. F. and higher to make it flexible or pliable, and capable of being pulled off the storage roll and inserted into the pipe to be rebuilt. This heating step and the necessary equipment and the time involved in heating the pipe as it is unwound, adds significantly to labor coats and time in the overall completion of a typical pipe lining job. This particular prior art problem concerning the heating step and the equipment required in addressing this problem associated with conventional rigid PVC pipe is discussed in U.S. Pat. No. 4,867,921 which sets forth the necessary heating step and hardware required in order to remove such rigid PVC pipe from storage means prior to use. In addition, the conventional rigid PVC does not provide for optimum expansion upon heating, and therefore cannot provide the desired tight molded fit in all pipe relining applications.
Accordingly, it is an object of this invention to provide improved polymeric compositions for lining of pipe which overcome the disadvantages and short-comings of the prior art described above. These and other objects will become readily apparent to those skilled in the art upon reading of the following description.